1. Field of the Invention
The present invention relates to static mixers useful for the continuous mixing of fluids, and particularly for mixing highly viscous fluids such as polymer melts.
2. The State of the Prior Art
Static mixing devices are particularly useful for homogenization of multi-component mixtures and the like. Static mixers also are useful in connection with heat exchangers and/or for plug flow reactors. These devices are simple and easy to use. A particular advantage is that static mixers have no moving parts and as a consequence present no particular sealing and/or maintenance difficulties.
It is known that devices of this type are often used for applications in polymer processing by extrusion or injection molding, involving large pressure drops across the mixer. This generally requires a rugged design involving the use of very thick material and reinforcing components. Smaller size elements may be made by precision casting of stainless steel or stellite. Elements may often be strengthened by welding or brazing individual components into a metal sleeve which then may function as a support for the element.
It is also desired that static mixer devices must generally be accessible for maintenance and cleaning and visual inspection after use. One previously known method to provide access permitting cleaning and inspection is to support individual elements with a satellite type ring as is shown in International Publication WO 95/09689. This construction, however, requires expensive precision casting and costly machined spacer rings. The crossbars must be relatively thick because the weak points are the unsupported, free crossbars.
For heavy duty polymer mixer applications in large pipes ( greater than 10xe2x80x3) with pressure drops of up to 100 bar, the elements must be welded into individual pipe sections. These sections must then be welded together to present the final mixer. This construction is again very expensive. Furthermore, due to the intricacy of the positioning of the components that are welded together, it is not possible to obtain 100% X-ray inspection of the welds. Accordingly increased wall thickness and hydraulic pressure testing is almost always required.
The problems and difficulties present in prior art devices are alleviated through the use of the present invention which provides a saddle element design for a static mixer which facilitates the manufacture and construction of the mixer as well as providing an ease of assembly and disassembly to thereby facilitate maintenance and cleaning. In particular, the simple design of the saddle element of the invention enables casting of the element as a monolithic structure whereby welding and brazing and the like are avoided.
In its broadest aspects, the invention provides a saddle element for a static mixer which comprises a generally ring-shaped support structure having a central axis, concentric inner and outer, radially spaced, circumferentially extending surfaces, and first and second axially spaced, generally parallel edge surfaces. The inner surface of the ring-shaped support structure defines a fluid flow path which extends along said axis. The edge surfaces are located in respective generally parallel transverse planes which are essentially perpendicular relative to said axis to facilitate stacking of the elements. The element also includes a plurality of elongated crossbars that are located in the flow path to cause intimate and thorough admixing of the fluids traveling along the flow path. In this regard, the crossbars each have a first end which is closer to the transverse plane of the first edge than to the transverse plane of the second edge and a second end which is closer to the transverse plane of the second edge than to the transverse plane of the first edge. The crossbars are strategically arranged in at least two separate intersecting oblique planes, each of which oblique planes is disposed at an angle relative to said axis.
In a desirable embodiment of the invention, crossbars are arranged in four separate oblique planes, which oblique planes are arranged in two separate pairs of oblique planes. The oblique planes of each pair thereof are disposed in generally parallel, laterally spaced relationship relative to one another. Moreover, the oblique planes of each pair of oblique planes are disposed so as to intersect the oblique planes of the other pair of oblique planes along lines which are generally perpendicular to said axis.
Preferably, at least two of said crossbars are arranged in each of the intersecting oblique planes, and the crossbars of each oblique plane are disposed in generally parallel, laterally spaced relationship.
In one preferred embodiment of the invention, the crossbars of the saddle element are arranged in an elongated, generally w-shaped array having a pair of spaced ends. Such array is disposed so as to extend laterally across the flow path with each end thereof being attached to the inner surface of the ring-shaped support structure. Another preferred aspect of the invention is that two of the oblique planes may be positioned so as to intersect at a line which is disposed essentially in the transverse plane of the first edge and which extends through the axis of the element. Preferably, the first ends of the crossbars of said two of said oblique planes are connected together at said line of intersection.
In a particularly preferred embodiment of the invention, the first end of a selected crossbar of a first oblique plane is attached to the inner surface of the ring-shaped support structure at a location adjacent said first edge, the second end of a selected crossbar of a second oblique plane is attached to the second end of the selected crossbar of the first oblique plane, the first end of a selected crossbar of a third oblique plane is connected to the first end of the selected crossbar of the second oblique plane, the second end of the selected crossbar of the third oblique plane is attached to the second end of a selected crossbar of a fourth oblique plane, and the first end of the selected crossbar of the fourth oblique plane is attached to the inner surface of the ring-shaped support structure at a location adjacent said first edge, said selected crossbars extending across the fluid flow path and presenting the desirable w-shaped array.
Ideally, in accordance with the invention, the intersecting oblique planes intersect at an angle of about 90xc2x0. That is to say, the oblique planes are disposed at an angle of about 45xc2x0 relative to the axis of the ring-shaped support structure. In further accordance with the principles and concepts of the invention, about 4 to 8 crossbars are arranged in each of said oblique planes.
The invention also provides a stacked static mixer structure comprising two of the saddle elements described above. These stacked saddle elements are arranged with the second edge surfaces thereof disposed in mated, contacting relationship. This also means that the second ends of the respective crossbars of the two elements are adjacent each other so as to present a generally double x-shaped configuration.
Preferably, the stacked static mixer structure includes four of the saddle elements. The saddle elements are arranged in a first group with the second edge surfaces of the ring-shaped support structures of two of the elements disposed in mated, contacting relationship, and in a second group with the second edge surfaces of the ring-shaped support structures of the other two elements also disposed in mated, contacting relationship. The two groups are stacked so that a first edge surface of a ring-shaped support structure of one group is disposed in mated, contacting relationship with a first edge surface of a ring-shaped support structure of the second group. The net result of this stacking is the provision of two stacked double x-shaped configurations. The four thusly stacked saddle elements provide the particularly preferred arrangement of the invention.